Security screens typically prevent unauthorised access to buildings through windows or doors, but often result in a prison-like appearance not compatible with ordinary office or other usage. In addition, some buildings, because of their location or the nature of the organisation occupying the building, are vulnerable to terrorist attack by explosives set off in front of the building.
WO 2002/006620 discloses a combination window blind and shutter which provides the advantages of high security combined with the appearance of ordinary vertical blinds. An additional advantage with this arrangement was found to be the possibility of automatic protection from bomb blast, inward movement of the window being protected causing the blind to close rapidly, thus reducing the risk of injury to the occupants of the building from broken glass and from the effects of the blast. These effects are enhanced by the combination of a sheet or film of plastics material extending between the window glass and the screen, as disclosed in WO 2008/059265. In order to ensure the maximum effectiveness of the use of the plastics sheet, it is necessary to space it accurately in relation to the blades of the blind, and there is a risk that incorrect installation would render the blind less effective. Also, the installation of the screen or blind may result in a reduced usability of the window or door, because of the need to install the additional plastics sheet.